Conventionally, there is known an optical module that includes an internal waveguide, a mirror section for changing an optical path, an optical element, and an external waveguide. The internal waveguide is provided in a trench formed in the surface of a substrate. The mirror section for changing the optical path is formed at the tip portion of the trench. In addition, the optical element is mounted on the surface of the substrate so as to oppose the mirror section. The optical element emits an optical signal to a core section of the internal waveguide via the mirror section, or receives the optical signal from the core section of the internal waveguide via the mirror section. The external waveguide has a core section optically coupled to the core section of the internal waveguide.
In such an optical module, in order to achieve bidirectional transmission or an increase in transmission capacity, it is necessary to use a plurality of the optical modules. As a result, a device including a plurality of the optical module is increased in size. To cope with this, it is desired to implement the optical module that is small in size, low in height, and capable of bidirectional or multi-channel transmission.
In order to implement such an optical module, it is conceived to mount a plurality of the optical elements on the surface of the substrate such that the optical elements are disposed close to each other. In this case, it is necessary to form the internal waveguides and the mirror sections at a small pitch so as to correspond to the interval of the plurality of the optical elements.
Conventionally, like an optical module described in Patent Document 1, there is proposed an optical module in which a plurality of optical transmission paths having different lengths from the end surface of the substrate are formed on the substrate, the optical elements are disposed close to each other at the ends of the individual optical transmission paths, and each of the optical elements is a light-emitting element or a light-receiving element. In this optical module, countermeasures against a cross-talk noise are not taken.
In a case where a plurality of the optical elements are close to each other, and the internal waveguides and the mirror sections are formed so as to reduce the pitch between the internal waveguides and the pitch between the mirror sections, leaked light from the optical element or scattered light from the mirror section or the internal waveguide enters the mirror section and the internal waveguide of the adjacent optical element, and the cross-talk noise is thereby generated. Such a cross-talk noise causes a transmission error. Consequently, it is requested to reduce the cross-talk noise as much as possible.
Patent Document 1: Japanese Patent Application Laid-open No. 2003-294964